This invention relates to a method of predetermining the gloss of a polyvinyl chloride (PVC) compound. In particular, it relates to preparing samples of a PVC compound having different molecular weight (MW) distributions, making articles from the samples, measuring the gloss of the articles, determining the relationship between the MW distribution and the gloss, and selecting a MW distribution from that relationship that will give the desired gloss.
PVC articles are made by molding PVC powders and plastisols. To enhance the appearance of the articles, manufacturers want to be able to control their gloss, so that their surfaces are as shiny or dull as desired. Gloss can be controlled by mixing PVC powders of different particle size distributions and by incorporating specialty resins or gloss control additives into the resin. These methods increase the cost of the materials needed to make the article and the number and complexity of the steps in the manufacturing process.
We have discovered that the gloss of articles made from mixtures of two PVC resins of different MWs falls to a minimum then increases again as the ratio of the resins in the mixture changes from 100% of one resin to 100% of the other resin. Remarkably, the minimum gloss is less than the gloss of articles prepared from 100% of either of those two resins. These results are surprising because it was expected that the gloss of articles made from such mixtures would be linearly proportional to the amount of each resin in the mixture (with the end points being the gloss of 100% of either resin). Because of this discovery, it is now possible to achieve a predetermined amount of gloss without using different particle size distributions, specialty resins, or gloss control additives.